The determination of coating performance with impedance measurements-I. Coating polymer properties

Modern coatings with new binders and pigmentation require new methods to optimize the formulation with respect to the protection of the metal substrate against corrosion. The methods normally used for accelerated weathering do not give information about the mechanism of failure of the coatings. Mechanistic information is necessary for a fast and more specific development of new coatings for various applications. Electrochemical impedance spectroscopy (EIS) can provide information. This article is part one in a series. The coating polymer properties and coatings performance are discussed. Moreover the experimental results are validated with respect to experimental errors. Models from the literature have also been included in the discussion. For the study of the curing mechanism and mechanical properties of the epoxy coatings the constant phase element (CPE) was found to be a valuable component in the equivalent circuit used for EIS. The values of the CPE parameters Y 11 and n are related to properties of the network of the coating polymer.